meta: Add on demand compilation of per target shader programs

meta: Add on demand compilation of per target shader programs

A call to glGenerateMipmap() follows the generation of a relevant
shader program in setup_glsl_generate_mipmap().

To support all texture targets and to avoid compiling shaders
everytime, per target shader programs are compiled on demand
and saved for the next call.

Fixes float-texture(mipmap.manual):
See Comment 6: https://bugs.freedesktop.org/show_bug.cgi?id=54296

NOTE: This is a candidate for stable branches.

Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Brian Paul <brianp@vmware.com>